Discharge for ball mills



Feb. 13, 19.34. E; VAN FELT I 1,946,511

DISCHARGE FoR BALL MILLS Filed oct. 5, 1931 :s sheets-'sheet 1 lllClttoz mg 3 Sheets-Sheet 2 E. L. VAN PELT DISCHARGE FOR BALL MILLSFiled-Oct. 5, 1931 Feb. 13, 1934.

Feb.13,1934. A EL, VAN FELT 1,946,511

DISCHARGE FOR BALLl MILLS Filed Oct. 5, 1951 3 Sheets-Shee'l'I 3 UNITEDSTA Patented Feb'. 13, 1934 DISCHARGE Foa BALL MILLS Elmer L. Van Pelt,Denver, Colo., assignor to American Ball-Mill Company, Denver, Colo., acorporation of Colorado Application October 5, 1931.

13 Claims.

This invention relates to improvements in rod or ball mills of the typeemployed for reducing or disintegrating materials containing minerals,for example, gold or silver ores and has reference more particularly toan improved screen and discharge device.

In the grinding of ores it is customary to feed the coarse ores into arotating cylinder having a crushing compartment in which are located l0suitable attrition members, such as balls or rods The material is fedinto the chambers through one of the trunnions on which the cylinder isrotated and leaves through an opening in the other trunnion. Interposedbetween the crush- 15 ing chamber and the outlet opening are a number ofgrates or grizzlies through which the ground ore must pass before it canbe discharged from the mill.

In mills of this type it has been customary to place the grates orgrizzlies transverselyof the mill and this makes it necessary to havethe mill lled to the innermost opening of the grate with attritionmembers and ore in order to get an eicient operation. The large loadcarried by the .mill makes it run very heavy and therefore it requiresan exceptionally large amount of power to operate it.

It is the principal object of this invention to produce a mill of thetype above described which shall be so constructed that efficientgrinding either wet or dry can be accomplished with a comparativelysmall number of attrition members and a small quantity of ore.

The above mentioned objects are accomplished principally through thesimple expedient of locating the grates with their surfaces lyingparallel with the axis of rotation instead of sub stantiallyperpendicular as has heretofore been the custom.

This invention, briey described, consists of a cylindrical shell whosetwo ends are closed by means of transverse heads each of which isprovided with a tubular trunnion. This shell is mounted for rotation inbearings suitably supported. The interior of the shell is lined withheavy cast liners which take up the wear and at the end of these linersadjacent the head through which. the material is discharged, a number ofgrates or grizzlies are arranged in such a way that they form anextension of the inner surface of the liners, so that the groundmaterial can pass directly from the surface of the liners onto thegrates and after passing through the grates, the material enters areception chamber that is connected with the outlet opening in theSerial No. 566.939

trunnion by means of passages that extend radially and through which thematerial can pass from the reception chamber to the discharge opening.The grates are protected against injury from the attrition members bymeans of 6" sector-shaped protector plates that extend radially from thecenter of rotation and terminate a short distance from the inner surfaceof the liners in such a manner that a passage is provided for the groundore and at the same time the attrition members are prevented fromentering that part directly above the grate.

Having thus briefly described the invention, the same will now bedescribed in detail, and for 'this purpose reference will be had to theaccom- 70 panying drawings in which the preferred embodiment thereof hasbeen illustrated, and in which:

Fig. l is a longitudinal section through the mill taken on averticalplane;

Fig. 2 is a transverse section taken on plane 2 2, Fig. 1;

Fig. 3 is a section through one of the grates and through the receptionchamber, taken on uneI 3, Fig. 2; 80

Fig. 4 is a perspective View, partly in section, showing one of thegrates and discharge sections with the sector-shaped 'protector plate inplace thereon;

Fig. 5 is a section taken on line 5 5, Fig. 4; and 95 Fig. 6 is a sideelevation looking in the direction indicated by arrows 6-6, in Fig. 5.

In the drawings reference numeral 1 indicates a cylindrical shell, theends of which are closed by transverse heads 2 and 3. Each of theseheads is 90 provided with a tubular trunnion 4, that is mounted forrotation in a bearing 5 supported on the vertical support 6. Arrangedaround the inner surface of the shell are a number of channels 7. Oneend of these channels is held in place by means of the end liners 8.These liners have been shown in transverse section in Fig. l, but havenot been shown in any other view because they do not form part of theinvention that is claimed in this application. Liners 8 aresector-shaped and 100 their upper ends which have been indicated byreference numeral 9 project into a groove in the inner end of thetrunnion. Pins 10 connect the outer edges of liners 8 to the channels inthe manner indicated in Fig. 1. Secured to the inner surface of thechannels are liner blocks 11 which may be made from cast iron or othersuitable material. These blocks are held in place by an arrangementcovered by United States patent but whiGh has not been shown because itforms no part of this invention. The space between the liner blocks iscaulked with oakum so as to prevent ground material from passing throughbetween the blocks. 'I'he space between the end liners 8 and theopposite ends of the liner blocks forms a crushing chamber within whichare located suitable attrition members 13 which may be balls or rods asmay be desired. The trunnion associated with head 2 is provided with aliner 14 whose inner surface is threaded and the material to be groundis fed into the crushing chamber through this opening in the directionindicated by the arrow. The opening in trunnion 4 of head 3 has a linercorresponding to liner 14, but which has a conical opening whose wallshave been indicated by reference numeral 15. This opening tapersinwardly and the inner end of the liner. which has been indicated byreference numeral 16 has a plurality of radial pockets 17 that are incommunication with the conical opening so that material may pass fromthe pockets into the discharge opening as indicated by arrow 18. Locatedbetween the head 3 and the adjacent ends of the liner blocks are gratesections 19. These sections form part of an assembly which has beenshown more in detail in Figs. 3 and 4, from which it will bc seen thatthe grates or grizzlies are secured to a hollow member which issubstantially sector-shaped. The lower end of this member is providedwith a bottom having section 20- that is parallel with the axis ofrotation and another section 21 that is upwardly inclined as shown mostclearly in Figs. 3 and 5. The inner end of section 21 terminates in anupwardly extending portion on which one edge of the grate rests.Extending upwardly from the outer end of bottom portion 20, is a wall 22and the edges of this wall are integral with the sides 23 and 24. Sides23 and 24 extend downwardly and are joined to the ends of sections 20,21 and-22. The inner edges of walls 23 and 24 are joined by wall 25 thatextends downwardly in the manner indicated in Fig. 5 and terminates in avertical portion 26 against which the inner edge of the grate abuts.Referring now to Fig. 6, it will be seen that the grates are removablyconnected with the assembly and the latter is provided with grooves 27for the reception of the ends of the grate. If a grate is broken or isto be replaced by one having diierent sized openings, this can bereadily accomplished by merely withdrawing the grate in a manner quiteapparent. Extending outwardly from sides 23 and 24 are lugs 28 which areperforated for the reception of bolts 29. The upper end of wall 25terminates a short distance below the upper ends of walls 23 and 24 andthe latter are provided with notches 30 with which the downwardlyprojecting flange 31 of the protector plate 32 cooperates. The flange 3lserves to support the protector plate and the latter is provided withinwardly extending lugs 33 that are adapted to engage in notches 34 onthe outer surface of wall 25. The protector plates are also providedwith two pairs of lugs 35 that are adapted to receive the head 36 ofbolts 29, and when the latter are tightened, the protector plates aresecurely held in place. One of the assemblies shown in Fig. 4 is placedbetween the inner end of the trunnion and each of the channels in themanner shown in Fig. 2. It will be observed from Fig. 1 that the innerend of the trunnion is provided with a groove 37 into which the upperend 38 of wall 22 extends. The interengagement between parts 37 and 38serves to hold the inner ends of these assemblies and for the purpose ofpositively securing them in place, a wedge 40 is provided for eachassembly. These wedges are held in place by hook bolts 41, one end 42 ofwhich projects through an opening in the webb of the channel and theother end of which is provided with a nut 43. By tightening the nut thewedge can be forced inwardly and will positively anchor the assembly inplace in a manner that is quite apparent from an inspection of Figs. 1and 3. From Fig. l it will be Aseen that the tubular lining of trunnion4 that is associated with head 3 extends inwardly a distancesubstantially equal to the width of walls 23 and 24, and the upper endsof the latter terminate adjacent the partitions between the compartments17.

At this point attention is called to Figs. 4, 5 and 6 from which it willbe seen that the lower ends of the protector plates 32 terminate a shortdistance above the upper surface of the grates so as to form openingsthrough which the ground ore may enter. From Fig. 6 it will be observedthat the lower edge of the sector-plate instead of being parallel withthe upper surface of the grate, is inclined with respect to this surfaceand therefore if a ball should become so badly worn that it will enterthe space above the grate, it will have an opportunity to escape fromthis position because it will roll from the narrowest part t0 the widestpart of this opening, when the mill is operating.

From Fig. 1 it will be seen that in addition to the wedges 40, theassemblies shown in'Fig. 4 are held in place by means of a circularmember 44, the center portion of which is conical as indicated bynumeral 45. The conical portion 45 extends into a conical opening in theliner and is secured to the latter by means of a bolt 46 and nuts 47.Member 44 extends over` the inner ends of the protector plates and inaddition to holding the assemblies in place, also forms a seal thatprevents l ground material from passing into the spaces between theassemblies.

Let us now assume that the machine shown in the drawings and describedherein is rotated by suitable means so that the attrition members willroll along the inner surfaces of the liner blocks, and that ore isintroduced into the crushing chamber through the opening in liner 14.The ore particles will mix with the attrition members and the latterwill grind them into a ne powder in a manner well understood. The groundmaterial will pass beneath the ends of the protector plate and into thespace above the grates, and from this space it will pass through thegrates and into the reception chamber. It is evident that the groundmaterial will not of itself travel upwardly into the opening in thedischarge outlet, but when the machine rotates, the material will becarried upwardly until it reaches a place above the center of themachine and will then fall through the action of gravity and travel inthe path indicated by arrows 48 and will pass outwardly through theoutlet opening.

It will be apparent from Fig. 1 that the protector plates prevent theattrition members from 1 entering the space directly above the gratesand therefore the grates need not be as strong as they would have to beif they were required to support the attrition members.

The mill described above and illustrated in the drawings differs fromthe ordinary mills of this type in several particulars, but the mostimportant is this, that the grates instead of extending substantiallytransversely of the drum or of the crushing chamber extend in thedirection of chords, when they are straight, or if they are curved thenthey may be concentric with the drum. The grates form extensions of theinner surface of the lining and the material passes through them in aradial direction as distinguished from the usual way in which the groundmaterial passes through the grates in the direction of the length of thedrum.

There are many advantages that result from this construction among themost important is this, that the pulp line can be kept very low andtherefore the minimum number of attrition members can be used as well asthe minimum amount of ore and this reduces the load and the powerrequired to operate the mill. The grates and grate assemblies can beindependently replaced if broken or worn. With mills of the ordinarytype when used for wet grinding, the discharge of ground products iseffected by the ilow of water through the grates carrying With it theparticles held in suspension. The particles which are too large to beheld in suspension naturally precipitate to the lowest level in themill, from which position escape is diicult because of insulcient flowof water at this level to overcome to any great extent the action ofgravity on these heavier particles.

The accumulation of these particles in the lower level of the mill tendsto restrict the ow of water through the grate at this level. It followsthen that the bulk of the water which is constantly being added to themill contents leaves the mill through the grates at a level above thatof the accumulation of larger particles; therefore, the heavierparticles remain in spite of the fact that they are small enough to passthrough the grate were they motivated in that direction.

When this mill is used for wet grinding, the iiow of water takes placeat the lowest level', thereby creating a positive current through thelower strata so to speak, which works in conjunction with gravity todischarge both the particles held in suspension and those heavier oneswhich may have precipitated, thereby increasing the discharge capacity.

Having described the invention what I claim as new is:

1. A mill of the character described, comprising a substantiallycylindrical shell provided at its ends with closure heads, each of theheads having a tubular trunnion concentric with the shell, the openingthrough one trunnion forming the feed and the opening through the otherforming the discharge, the inside of the shell having liners which formthe outer wall of a crushing compartment, suitable attrition bodies inthe crushing compartment, a plurality of substantially triangular hollowgrate assemblies located between one end of the lining and the dischargehead, each assembly having an outer and an inner Wall, a portion of theinner wall being inclined towards the outer wall, the base being widerthan the distance between the lower ends of the inner and outer wallsand provided with an upper edge spaced from the lower end of the innerwall so ing the discharge, the inside of the shell, having liners whichform the outer wall of a. crushing compartment and terminating a shortdistance from the inside of the discharge closure head. suitableattrition bodies in the crushing compartment, a plurality ofsubstantially triangular hollow grate assemblies located between one endof the lining and the discharge head, each assembly having an inner andan outer wall the lower portion of the inner wall being inclined towardsthe outer wall, the base being wider than the distance between the lowerends of the inner and outer walls and provided with an upper edgespacedfrom the lower end of the inner wall so as to provide an opening,a grate located in the opening, means for securing each assembly inplace and a substantially triangular protector plate secured to theinner surface of .each assembly, the base oi each plate terminating ashort distance above the plane of the upper surface of the grate.

3. A grate assembly for use in mills of the character described,comprising, a substantially triangular hollow member having an outerwall, two side walls, an inner wall and a bottom, the inner wall havingits lower end nearer to the outer wall than its upper end, the bottomhaving an upwardly extending edge spaced from the lower end of the innerwall whereby an opening is formed, and a grate located in the opening.

4. A grate assembly for use in mills of the character described,comprising a substantially triangular hollow member having an outerwall, two side walls, an inner wall and a bottom, the inner wall havingits lower end nearer to the outer wall than its upper end, the bottomhaving an upwardly extending edge spaced from the lower end of the innerwall whereby an opening is formed, a grate located in the opening and asubstantially triangular guard plate secured to the inner surface of theinner wall.

5. In a.machine of the class described having a drum comprising acylinder with an intake and a discharge head, a plurality of grateassemblies adjacent the discharge head, the discharge head having atubular trunnion, a portion of which extends to the inside of the head,said portion having a groove in its outer surface, each of the grateassemblies having a portion projecting into the groove and meanscomprising wedges and anchoring bolts for forcing the assemblies againstthe head and against the trunnions.

6. A mill of the character described, comprising, a substantiallycylindrical shell mounted for rotation about its own axis, the mountingmeans comprising two hollow trunnions, one of which provides a feedopening and the other a discharge opening, the inside of the shellform-I ing `a crushing compartment, suitable attrition bodies in thecrushing compartment, the inner surface of t-he shell having removableliners, terminating short of the discharge end, gra-te sections betweenthe ends of the liners and the discharge end, the inner surfaces of thegrates being substantially parallel with the axis of rotation, the outersurfaces of the grate sections being spaced from the inside of thecylindrical shell, attrition bodies in the crushing compartment. guardplates between the crushing compartment and the grates. and meanseffective on the rotation of the shell for conveying the material thathas passed through the grates to the discharge opening.

'7. A mill of the character described, comprising a substantiallycylindrical shell provided at its ends with closure heads, each of theheads having a tubular trunnion concentric with the shell, the openingthrough one trunnion forming the feed and the opening through the otherforming the discharge, the inner surface of the shell having removableliners extending from the end closure having the feed opening andterminating a short distance from the end closure having the dischargeopening, grates located in the shell between the ends of the liners andthe discharge end closure, the inner surfaces of the grates beingsubstantially parallel with the axis of rotation, the outer surfaces ofthe grates being spaced from the inside of the shell, guard platesbetween the liner surfaces and the grates, attrition bodies in thecompartment whose wall is formed by the inner surfaces of the liners,and means for transferring the ground material that has passed throughthe grates to the discharge opening.

8. A mill of the character described, comprising a substantiallycylindrical shell provided at its ends with closure heads, each of theheads having a tubular trunnion concentric with the shell, the openingthrough one trunnion forming the feed and the opening through the otherforming the discharge, removable liners extending from the intake headto a point some distance from the inside of the discharge closure head,grates located in the space between the ends of the liners and theinside of the discharge closure head, the inner surfaces of the gratesbeing in substantial alignment with the inside surfaces of the liners,the outer surfaces of the grates being spaced from the inside surfacesof the liners, the outer edge of the guard plate being locatedsubstantially at the juncture of the liners and the grates, attritionmeans in the compartment included between the intake end closure and theguard plate, and means for transferring the material that has passedthrough the grates to the discharge opening as transferring the materialthat passes through the grate to the discharge opening in the dischargehead when the cylinder is rotated.

10. In a mill of the character described, the combination of a rotarycylindrical shell, a feed head and a discharge head therefor, each headhaving an opening, the inner surface of the shell being provided withremovable liners which terminate short of the discharge head, grateslocated between the discharge head and the adjacent end of the liners,the grates forming extensions of the inner surface of the lining, theoutside surfaces of the grates being spaced from the inside of theshell, means for holding the grates in position, means for transferringthe ground material that has passed through the grates to the dischargeopening, and protector plates extending radially from the center andterminating adjacent the lining surface for protecting the grates.

ll. A ball mill having a crushing chamber provided with a protectivelining, a plurality of grates whose surfaces form extensions of theinner surface of the lining and which have their inner surfacessubstantially parallel with the axis of rotation, a radial protectorplate extending from near the center of chamber to a point adjacent theinner surface of the liners, but terminating short of this surface, andattrition members in the crushing chamber.

12. A ball mill comprising a cylindrical drum having a tubular intakehead at one end and a discharge head provided with a tubular trunnion atthe other, the inner surface of the drum being provided with a liningterminating short of the discharge head, grates located in the drumbetween the end of the lining and the discharge head, the grates formingextensions of the inner surface of the lining, and means fortransferring the material that passes through the grates to the innerend of the tubular trunnion in the discharge head when the drum isrotated.

13. A ball mill, or the like, having a substantially cylindrical shellmounted for rotation aboutits axis, one end of the inner surface of theshell having removable liners and the other end a separate substantiallycylindrical grate section located Within the shell and spaced from theinside thereof through which the material can pass 'in a radialdirection, and means for raising the ground material to the center ofthe shell and discharging it as the shell rotates.

ELMER L. VAN PELT.

